[mle] fix processing of CSL TLVs

[abtink]

This commit contains fixes and enhancements related to processing of CSL Channel TLV and CSL Clock Accuracy TLV in MLE messages:

• Updates/adds IsValid() method to check if TLV is well-formed. In particular, we check the TLV length to be at least the expecte length (but can be larger) to allow for future changes to the TLV format (adding new fields while remaining backward compatible).

• Ensure to verify that the read TLV is valid before using its content.

• Fix processing of Accuracy TLV in HandleChildUpdateResponse() (where we could use incorrect values if TLV was not present).

[codecov[bot]]

Codecov Report

Merging #8004 (308f683) into main (ba14836) will decrease coverage by 0.00%. The diff coverage is 71.42%.

@@            Coverage Diff             @@
##             main    #8004      +/-   ##
==========================================
- Coverage   85.44%   85.43%   -0.01%     
==========================================
  Files         505      505              
  Lines       70093    70103      +10     
==========================================
+ Hits        59888    59892       +4     
- Misses      10205    10211       +6     

Impacted Files	Coverage Δ
src/core/thread/mle_router.cpp	85.57% <50.00%> (-0.26%)	:arrow_down:
src/core/thread/mle.cpp	89.39% <81.81%> (+0.04%)	:arrow_up:
src/core/thread/mle_tlvs.hpp	100.00% <100.00%> (ø)
src/core/thread/mesh_forwarder.cpp	87.73% <0.00%> (-0.62%)	:arrow_down:
src/lib/spinel/radio_spinel_impl.hpp	85.95% <0.00%> (-0.39%)	:arrow_down:
src/core/thread/router_table.cpp	92.93% <0.00%> (-0.36%)	:arrow_down:
src/posix/platform/hdlc_interface.cpp	51.49% <0.00%> (-0.34%)	:arrow_down:
src/core/mac/mac.cpp	89.57% <0.00%> (-0.30%)	:arrow_down:
src/core/coap/coap.cpp	79.77% <0.00%> (ø)
... and 7 more

[size-report[bot]]

Size Report of OpenThread

Merging #8004 into main(ba14836b68e7eb8a00248f31bbd65a9a3edfb320).

name	branch	text	data	bss	total
ot-cli-ftd_1.1	main	462496	780	60772	524048
	#8004	462528	780	60772	524080
	+/-	+32	0	0	+32
ot-cli-mtd_1.1	main	381904	780	50564	433248
	#8004	381904	780	50564	433248
	+/-	0	0	0	0
ot-ncp-ftd_1.1	main	444220	780	59752	504752
	#8004	444252	780	59752	504784
	+/-	+32	0	0	+32
ot-ncp-mtd_1.1	main	366372	780	49544	416696
	#8004	366372	780	49544	416696
	+/-	0	0	0	0
ot-rcp_1.1	main	58136	564	19964	78664
	#8004	58136	564	19964	78664
	+/-	0	0	0	0
libopenthread-cli-ftd.a_1.1	main	45925	0	4244	50169
	#8004	45925	0	4244	50169
	+/-	0	0	0	0
libopenthread-cli-mtd.a_1.1	main	38548	0	4244	42792
	#8004	38548	0	4244	42792
	+/-	0	0	0	0
libopenthread-ftd.a_1.1	main	242862	20	39090	281972
	#8004	242882	20	39090	281992
	+/-	+20	0	0	+20
libopenthread-mtd.a_1.1	main	175930	20	28882	204832
	#8004	175930	20	28882	204832
	+/-	0	0	0	0
libopenthread-ncp-ftd.a_1.1	main	31597	0	5852	37449
	#8004	31597	0	5852	37449
	+/-	0	0	0	0
libopenthread-ncp-mtd.a_1.1	main	26441	0	5852	32293
	#8004	26441	0	5852	32293
	+/-	0	0	0	0
libopenthread-rcp.a_1.1	main	8894	0	4988	13882
	#8004	8894	0	4988	13882
	+/-	0	0	0	0
libopenthread-radio.a_1.1	main	15939	0	174	16113
	#8004	15939	0	174	16113
	+/-	0	0	0	0
ot-cli-ftd_1.3	main	485280	780	70468	556528
	#8004	485296	780	70468	556544
	+/-	+16	0	0	+16
ot-cli-mtd_1.3	main	397072	780	51820	449672
	#8004	397072	780	51820	449672
	+/-	0	0	0	0
ot-ncp-ftd_1.3	main	465964	780	69440	536184
	#8004	465980	780	69440	536200
	+/-	+16	0	0	+16
ot-ncp-mtd_1.3	main	380124	780	50792	431696
	#8004	380124	780	50792	431696
	+/-	0	0	0	0
ot-rcp_1.3	main	60464	564	20532	81560
	#8004	60464	564	20532	81560
	+/-	0	0	0	0
libopenthread-cli-ftd.a_1.3	main	48783	0	4244	53027
	#8004	48783	0	4244	53027
	+/-	0	0	0	0
libopenthread-cli-mtd.a_1.3	main	40812	0	4244	45056
	#8004	40812	0	4244	45056
	+/-	0	0	0	0
libopenthread-ftd.a_1.3	main	261802	20	48242	310064
	#8004	261818	20	48242	310080
	+/-	+16	0	0	+16
libopenthread-mtd.a_1.3	main	187773	20	29594	217387
	#8004	187773	20	29594	217387
	+/-	0	0	0	0
libopenthread-ncp-ftd.a_1.3	main	33427	0	5852	39279
	#8004	33427	0	5852	39279
	+/-	0	0	0	0
libopenthread-ncp-mtd.a_1.3	main	27807	0	5852	33659
	#8004	27807	0	5852	33659
	+/-	0	0	0	0
libopenthread-rcp.a_1.3	main	9060	0	4988	14048
	#8004	9060	0	4988	14048
	+/-	0	0	0	0
libopenthread-radio.a_1.3	main	16819	0	206	17025
	#8004	16819	0	206	17025
	+/-	0	0	0	0